Breech cap for applying signals to explosive cartridges



Jan. 20, 19% c. A. DAMM Mwsaz BREECH CAP FOR APPLYING SIGNALS TO EXPLOSIVE CARTRIDGES Filed Jan. 25, 1968 13 7 so 42 l v f/ 43 33 31 200 5 47 k 21 41 I WELD 70 a 1 30a V N r 55 so 30 4e T0 SIGNAL SOURCE INVENTOR.

CARL A. DAM M United States Patent l 3,490,332 BREECH CAP FOR APPLYING SIGNALS T0 EXPLOSIVE CARTRIDGES Carl A. Damm, Upper Black Eddy, Pa., assignor to the United States of America as represented by the Secretary of the Navy Filed Jan. 25, 1968, Ser. No. 700,603 Int. Cl. F41f 13/08 US. CI. 89-28 13 Claims ABSTRACT OF THE DISCLOSURE A breech cap for applying an electrical signal to the electrode of an explosive cartridge including a cartridge abutting, ground contact plate adapted for closing a cartridge-receiving chamber, a coaxially arranged, springloaded primary contact, and a metal pressure dome filled with and sheathed with polyurethane. The dome is mechanically and electrically connected between the ground contact and the grounded shield of a signal providing conductor which, in turn, is electrically connected with the primary contact.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF INVENTION The use of store racks including pyrotechnic ejector assemblies similar to those disclosed in UJS. Patent No. 3,036,852 to C. W. Mullison issued May 29, 1962, and in US. patent application, Ser. No. 657,738 filed July 31, 1967, by Carl A. Damm for Ejector Assembly with Lockable Store-Engaging Presser Foot and now Patent No. 3,431,824 has created a need for a reusable electrical breechcap of rugged construction which is able to withstand explosive cartridge misfires. Misfires subject known electrical breech caps to damage which may not readily be ascertainable upon inspection. Subsequent use of damaged breech caps results in failure of the ejector assembly to perform its intended function.

SUMMARY OF INVENTION It is the general purpose of this invention to provide a reusable, explosion-proof breech cap adapted for providing an electrical firing signal to explosive charges, briefly, the general purpose of the invention is accomplished by providing a breech cap having a pressure dome to which is mechanically aflixed a ground contact member which is adapted for closing the breech of a cartridge receiving chamber and carries a primary contact mechanism arranged to contact the electrode of an electrically fireable exposive cartridge. More particularly, the invention contemplates that the pressure dome be mechanically fixed to a ground contact plate having a spring-loaded primary contact carried within an insulated tube having a piston-like closure and being electrically connected with a signal lead. It is additionally contemplated that the interior of the pressure dome be filled with a shock absorbing, electrically insulating elastomer such as polyurethane which, further, is integrally formed with a polyurethane sheath. It also is contemplated that the cap further include a tensioned O ring which extends about the pressure dome and bears against a rotatable mechanical coupling adapted for connecting the breech cap to close the cartridge receiving chamber.

3,490,332 Patented Jan. 20, 1970 BRIEF DESCRIPTION OF DRAWING DESCRIPTION OF PREFERRED EMBODIMENT Referring to the figure, the breech cap, generally designated 10, is adapted for mechanical connection to close a tubular barrel 11 of a pyrotechnic ejector assembly (not shown) within which is received an explosive cartridge 12. The aluminum encased cartridge 12 is of the type which may be actuated by the application of an electrical signal to an electrode 13 arranged coaxially of flanged end 14 of the cartridge 12 in an insulating bushing 15. The barrel 11 terminates in an externally threaded portion 16 and provides an annular seat for the flanged end 14 of the cartridge 12.

More particularly, the cap 10 includes an electrically conducting ground contact plate 20 having a generally circular configuration and made of strainless steel. The plate 20 further has an integrally formed, cylindrical boss 21 extending coaxially away from a cartridge adjacent end thereof, a bore 20a coaxially extending therethrough and through the boss 21, and a coaxially arranged annular groove 20b formed in the extended end of the boss 21 for a purpose hereinafter explained. Three stainless steel ground contact pins 22 each terminating in a conical point are fixed in a symmetrical arrangement about the bore 20a to project from the plate 20 for establishing a good electrical contact with the metallic casing of the flanged end 14 of the cartridge 12.

The cap 10 also includes an electrically conductive, tubular pressure dome 30 which has a flange 31 radially extending outwardly of one end and which has a hemispherical portion 32 closing the other end. The dome 30 has an interior periphery of circular configuration which is sized to receive the boss 21 so that the plate 20 abuts the flange 31 of the dome 30 and closes the flanged end of the dome 30. Electrical and mechanical connection of the pressure dome 30 to the plate 20 is established by three or four symmetrically arranged spot welds as at 33. The pressure dome 30 further has four symmetrically arranged apertures 30a extending through its lateral periphery adjacent the grooved end of the boss 21 for a purpose hereinafter explained.

An electrically conductive tube 40 of brass which is received within a tubular sheath 41 made of an insulating material such as Lexan made by the General Electric Company is tightly arranged within the bore 20a of the plate 20 and boss 21. The cartridge adjacent end of the sheath 41 is closed by an inwardly projecting flange which forms a coaxially apertured stop 42' for a cylindrical primary contact member 43 which is made of electrically conductive material such as stainless steel and which is received for sliding electrical contact with the inner periphery of the tube 40. The primary contact member 43 includes a conically pointed contact pin 44 which coaxially projects therefrom and through the aperture of the stop 42 to establish a good electrical contact with the electrode 13 of the cartridge 12. The other end of the tube 40 which extends toward the hemispherical portion 32 of the dome 30 is closed by a tightly fitting cylinder 45 made of, electrically conductive material such as brass and having an integrally formed flange 46 which is seated against the end of the tube 40 and which extends radially beyond the sheath 41 and toward the enveloping pressure dome 30. The confronting ends of the primary contact member 43 and the cylinder 45 include coaxially projecting bosses 47 and 48 around which are tightly received in good mechanical and electrical contact therewith the end of an electrically conductive, compressed coil spring 49 which normally urges the tapered contact pin 44 of the primary contact member 43 to puncture through any oxidation layer formed on the confronting electrode 13 of the cartridge 12 and establish good electrical contact therewith.

An electrical signal of voltage and power suitable for firing the electrically responsive explosive cartridge 12 is supplied from a remote point such as the cockpit of an aircraft to the cap via a signal lead 50 having a stranded conductor 51, an inner sheath 52 of insulating material such as Teflon made by DuPont & Company, an encircling grounded shield 53 such as of braided, tinned copper, and an outer protective, insulating jacket 54 made of a material such as polyurethane. The end of the conductor 51, having been stripped of its insulating sheath 52, its grounded shield 53 and its protective, insulating jacket 54,'is inserted into electrically conductive roll pin 55. The roll pin 55, which may be flared at one end to facilitate receiving the stranded conductor 51, is inserted through a coaxial bore extending through the sheathed tube 40 and the cylinder 44 for establishing good electrical contact with the contact member 43 via the tube 40 and via the cylinder 45 and spring 49. Both of the protruding ends of the roll pin 55 are crimped to further establish good electrical contact and to prevent withdrawal of the roll pin 55 and the conductor 51.

An end of the lead from which the jacket 54 has been removed is threaded through a aperture 32a formed in the hemispherical portion 32 of the pressure dome 30 and through a flanged electrically conductive eyelet 56 made of brass. A sufficient length of the grounded shield 53 has been stripped away to leave a coil or loop 50a of the insulation ensheathed conductor 51 which extends from the eyelet 56 and the dome 30 to the roll pin 55. The end of the grounded shield 53 is electrically and mechanically aflixed to the hemispherical portion 32 of the pressure dome 30 by the eyelet 56 which is inserted between the shield 53 and the inner insulating sheath 52 to force the shield 53 radially outward to engage the boundary of the aperture 32a in the dome 30. The end of the grounded shield 53 is flared by the eyelet 56 and is pressed into engagement with the interior pheriphery of the hemispherical portion 32 of the dome 30 by the flanged portion of the eyelet 56. The good electrical contact established thereby between grounded shield 53 and the dome 30 and also the plate 20 assures that spurious electrical signals will not cause an untimely firing of the cartridge 12.

The cap 10 further includes a tubular coupling member 60 whose interior periphery at one end is threaded for connection to the threaded portion 16 of the cartridge 11.

, The other end of the coupling member 60 terminates in an inwardly extending flange 61 which defines an aperture through which the coaxially arranged pressure dome 30 is received and which provides a seat for the flange 31 of the pressure dome 30. A tensioned O ring 70 made of an elastomer such as butyl rubber encircles the lateral periphery of the pressure dome 30 and bears against the flange 61 of the rotatable coupling member 60 to urge it into abuttment with the flange 31 of the pressure dome 30. The interior of the pressure dome 30 is filled with an insulating elastomer such as polyurethane 80 which extends to fill the annular groove 20b in the boss 21 and extends through the ports 30a to form an exterior sheath 81 about the dome 30 which abuts the O ring 70. The polyurethane sheath 81 extends about the outer periphery of the pressure dome 30 and its hemispherical portion 32 and terminates in a pigtail 82 which extends along the grounded shield 53 and beyond the terminus of the jacket 54 of the lead 50. The polyurethane 80 in the pigtail 82 fills the interstices of the grounded shield 53 and, further, mechanically bonds the lead 50 to the cap 10. The loop 50a of the lead 50 is encased in the polyurethane 80 and further prevents withdrawal of the lead from connection with the cap 10. Also, mechanical vibrations which might be transmitted along the lead 50 are blocked by the loop 50a.

One convenient manner of assembling the cap 10 contemplates that the jacket 54 of the lead 50 be stripped away to expose a length of the grounded shield 53 and that a shorter length of the grounded shield 53 be stripped away to expose a suitable length of the insulated conductor 51 to form the coil 50a whose uninsulated free end is to be inserted through the roll pin-5S. The lead 50 is threaded through the O ring 70 and the flanged end of the coupling 60. The end of the grounded shield 53 is mechanically fixed to the pressure dome 30 by forcing the eyelet 56 between the grounded shield 53 and the underlying insulating sheath 52 threaded therethrough and into the aperture 32a. The sheathed tube 40 having the spring-loaded primary contact member 43 therewithin is force fit or otherwise fixed within the bore 20a of the ground contact plate 20 and boss 21. The roll pin 55 having received the end of the conductor 51 is inserted through the transverse bores formed in the sheathed tube 40 and the cylinder 45, and the ends of the roll pin 55 protruding from either side of the sheath 41 are crimped to prevent withdrawal of the conductor 50 therefrom and to assure a good electrical connection of the conductor 51 with the tube 40 and the cylinder 45 through the roll pin 55. The loop 50a is formed and positioned within the pressure dome 30 by insertion of the boss 21 of the plate 20 into the pressure dome 30 fixing the plate 20 against the flange 31 of the pressure dome 30. The pressure dome 30 is inserted into the coupling 60 so that the flange 31 of the pressure dome 30 seats against the flange 61, and the O ring 70 is rolled over the lateral periphery of the pressure dome 30 to a position forcing the coupling member flange 61 to seat against the dome flange 31. The cap 10 is then placed in a mold and a polyurethane delivery tube (not shown) is inserted through one of the apertures 30a, and the interior of the pressure dome 30 is filled with polyurethane under pressure. The delivery tube is withdrawn from the aperture 30a so that the exterior polyurethane sheath 81 about the pressure dome 30 and the pigtail 82 may be formed. The polyurethane 80 fills the interstices in the grounded sheath 53 and helps to form a strong mechanical bond of the lead 50 the cap 10. It is contemplated that projections (not shown) could be integrally molded with the sheath 81 to facilitate gripping the ensheathed dome 30 of the cap 10. The O ring 70 prevents seepage of flowable polyurethane into the interface between the coupling member 60 and the pressure dome 30 during the molding process.

It is contemplated, of course, that the coupling member 60 could be modified for use with the particular ejection assemblies shown in the above noted Mullison patent and Damm application which have a recessed cartridge seat and an internally threaded barrel. For example, the relatively rotatable coupling 60 would have a lateral periphery which is threaded and extends only as far as the plate 20.

Addtionally, it is contemplated that the boss 21 of the ground contact plate 20 need not extend radially at its innermost end to engage the inner lateral periphery of the dome 30. For example, the annular wall defining the outmost boundary of the groove 20b need not be included. The torturous interfaces between the boss 21 and the sheathed tube 40 and between the boss 21 and the polyurethane 80 undergo at least one turn.

Thereby is provided a breech cap which is explosion proof and is well adapted for withstanding the wear and tear of continued usage. Should a cartridge misfire and explosive gases seep along the bore 20a between the interface of the boss 21 and the sheath tube 40, the gases will be directed toward the flange 46 of the cylinder 45 causing the flange 46 to tend to compress the polyurethane 80 against the interior of the hemispherical portion 32 of the dome 30. The shock mitigating characteristics of the polyurethane 80 will dissipate the destructive forces of the explosion. Additionally, the explosive gases will not tend to rupture the polyurethane 80 because they tend to seep, if at all, along the bore a and along the boundary of the annular channel 2017. Since the direction of any seepage is to ced to undergo a 180 turn, much of the explosive force is further dissipated.

The O ring 70 may be stretched out of its position between the sheath 81and the coupling 60 and rolled back to enable reciprocation of the coupling flange 61 along the lateral periphery of the pressure dome to eliminate powder particles or other residue which might tend to seep into the interface between the interior lateral periphery of the coupling member 60 and the lateral peripheries of the plate 2.0 and the dome 30. The ring 70 also prevents dust and dirt particles from clogging the interface of the coupling 60 with the plate 20 and the dome 30.

As the coupling 60 is threaded onto the cartridge chamber 11, the ground contact pins 22 are firmly driven into the confronting end of the cartridge 12 to establish a firm electrical contact therewith. Similarly, the spring 49 forces the primary contact pin 44 to establish a firm electrical contact with the cartridge 12 and assure that the cartridge 12 will fire when an appropriate firing signal is applied to the lead 50.

What is claimed is: i

1. A breech cap for transmitting an electrical signal to an electrode of an electrically actuatable explosive cartridge comprising:

ground contact means for electrically contacting the cartridge;

primary contact means carried by said ground contact means for electrically contacting the electrode;

pressure dome means including a tube closed at one end by and connected to said ground contact means and closed at the other end by a hemispherical portion aligned with said primary contact means, said hemispherical portion being spaced from said ground contact means and said primary contact means; and

an elastomer having insulating and shock mitigating characteristics and filling the interior of said pressure dome means.

2. A breech cap for transmitting an electrical signal to an electrode of an electrically actuatable explosive cartridge comprising:

ground contact means for electrically contacting the cartridge, said ground contact means including a plate member having formed therethrough a bore;

primary contact means for electrically contacting the electrode carried by said ground contact means within said bore and being insulated from said ground contact means, said primary contact means including a flange extending outwardly of an extension of the boundary of said bore; and

pressure dome means connected to said ground contact means and terminating in a hemispherical portion aligned with said primary contact means, said dome means having said flange of said primary contact means positioned therewithin.

3. Apparatus according to claim 2 wherein:

a side of said ground contact member confronting said hemispherical portion of said dome means includes formed therein an annular groove arranged coaxially outwardly of an inner terminus of said bore; and

said apparatus further comprises an elastomer having insulating and shock mitigating characteristics and filling the interior of said pressure dome and said groove in said ground contact member.

4. Apparatus according to claim 2 wherein:

said dome means comprises a tube closed at one end by said plate member and closed at the other end by said hemispherical portion, said dome means having an aperture formed therein; and

said apparatus further comprises conductor means electrically connected to said primary contact means and threaded through said aperture of said pressure dome means, said conductor means having a grounded shield electrically and mechanically connected to said dome means.

5. Apparatus according to claim 4 wherein:

said conductor means includes an insulated conductor ensheathed by said grounded shield and extending through said dome aperture for electrical connection to said primary contact means; and

said apparatus further comprises a flanged eyelet having threaded therethrough said insulated conductor and interposed between said insulated conductor and said grounded shield for forcing said grounded shield to engage the boundary of said pressure dome aperture and the adjacent interior periphery of said pressure dome to establish good mechanical and electrical contact therewith.

6. Apparatus according to claim 5 wherein:

the portion of said insulated conductor extending from said eyelet to said primary contact means forms a loop interposed generally transversely of an axis extending through said pressure dome aperture.

7. Apparatus according to claim 2 wherein said primary contact means comprises:

a tube made of electrically conducting material extending generally coaxially with the axis of said ground contact means bore;

an insulating sheath interposed between said tube and said ground contact member and terminating at a cartridge confronting end in a contact member stop having a coaxial bore extending therethrough;

a primary contact member arranged within said tube for sliding electrical contact therewith and having a contact pin formed for protrusion through said coaxial bore of said insulating means stop to electrically contact the electrode of the cartridge;

a cylinder having said outwardly extending flange and positioned for closing the end of said tube opposite said stop; and

a coil spring interposed within said tube between said contact member and said cylinder for urging said contact member toward engagement with said stop of said insulating sheath.

8. Apparatus according to claim 7 wherein:

said dome means comprises a tube closed at one end by said ground contact plate member and closed at said other end by said hemispherical portion, said portion being spaced from said plate member and said primary contact means; and

said apparatus further comprises an elastomer having insulating and shock mitigating characteristics and filling the interior of said pressure dome.

9. Apparatus according to claim 8 wherein said pressure dome tube further includes an aperture formed therein for providing communication between the exterior and the interior of said pressure dome tube and terminates at said one end in an outwardly extending flange seated against and fixed to said ground contact plate member; and wherein said apparatus further comprises:

a coupling member formed for connection to a cartridge receiving chamber and having an inwardly extending flange through which is rotatably received said pressure dome tube and said plate member;

a tensioned O ring made of an elastomeric material and positioned about said pressure dome tube to cause said flange of said coupling .member to abut said flange of said pressure dome tube; and

a sheath of said elastomer extending through said aperture and about the outer periphery of said pressure dome means and engaging the confronting periphery of said O ring.

10. Apparatus according to claim 9 wherein said dome means includes another aperture and said apparatus further comprises:

a signal lead including an insulated conductor threaded through said other dome aperture and electrically connected to said primary contact tube, a braided, grounded shield ensheathing said insulated conductor and terminating in an electrical and mechanical connection with said dome means, and a projective jacket ensheathing a portion of said shield and terminating in spaced relation to the exterior of said dome means; and

said sheath of elastomer extending from said dome means along said lead beyond the terminus of said jacket and filling interstices in said braided, grounded shield.

11. Apparatus according to claim 10 wherein:

said ground contact means includes a boss having said bore formed coaxially therethrough, said boss extending into said dome means from said plate member and having a surface in contact with said elastomer and positioned radially outwardly of said bore and radially inwardly of said dome means and extending generally parallel with said bore.

12. A breech cap for transmitting an electrical firing signal to an electrode of an electrically actuatable explosive cartridge comprising:

hollow pressure dome means;

ground contact means for electrically contacting the cartridge and being fixed to and closing said pressure dome means, said ground contact means having a bore extending therethrough;

primary contact means being mounted in said bore, being insulated from said ground contact means and being spaced from and extending within said dome means, said primary contact means including at an outer end a primary contact for electrically contacting the electrode and including at an inner end a flange outwardly extending transversely of an extension of said bore;

signal lead means extending through said dome means and electrically connected to said primary contact; and

an elastomer having insulating and shocking mitigating characteristics filling the interior of said pressure dome.

13. Apparatus according to claim 12 wherein said primary contact means comprises:

a tube made of electrically conductive material, re-

ceived in said bore and having an exterior insulating sheath terminating at one end in an inwardly projecting flange partially closing one end of said tube;

said primary contact electrically contacting and being slidably received within said tube and having a contact point protruding through said inwardly projecting flange for contacting the cartridge electrode;

an electrically conductive cylinder closing the other end of said tube and having said outwardly extending flange radially extending therefrom and beyond the periphery of said ensheathed tube;

a roll pin made of electrically conductive material, extending transversely through both said tube and said cylinder and being electrically connected to said signal lead means; and

a spring entrapped between said primary contact pin and said cylinder for normally urging said contact point to protrude for contacting the cartridge electrode.

References Cited UNITED STATES PATENTS 1,108,717 8/1914 Davis 8928 2,681,701 6/1954 Schlumberger 10246 X 2,789,467 4/1957 Rosenthal 891 3,018,733 1/1962 Johnson 102--70.Z 3,232,168 2/1966 Mangeng et al 8928 X 3,251,216 5/1966 Broske 10246 X FOREIGN PATENTS 1,087,469 8/ 1954 France.

VERLIN R. PENDEGRASS, Primary Examiner US. Cl. X.R. 10246 

